Conventional process for fabricating a thin film light emitting diode (TF-LED) roughly contains two phases. The first phase is to grow epi layers on a growth substrate and thus forming the epi wafer. The growth substrate can either be made of sapphire or silicon carbide. The number of epi layer can be designed according to the need. The second phase is to bond the epi wafer to a support substrate (such as a sub-mount or a packaging substrate), to remove the growth substrate, and to perform further semiconductor processes such as etching, photolithographing, development and phosphor coating. During the fabricating process of TF-LED, it's difficult to measure the photoelectric properties, such as the characteristics of current-voltage or spectrum of the epi wafer. Accordingly, said photoelectric properties of TF-LED are inspected and measured after the completion of two-phase process of TF-LED.
In the above process, particularly in the second phase of making a TF-LED, the semiconductor process is performed onto the entire epi-layer bonded with the support substrate. The photoelectric properties interim are hardly to be inspected, leading to a poor yield rate of TF-LED to 50% or even worse. More specifically, only 50% or fewer chips, though bonded with the support substrate, could meet the predetermined photoelectric properties. This means that all the chips, whether they meet the pre-determined photoelectric properties or not, have to undertake the subsequent fabrication process. For the chips that fail to meet the required photoelectric properties, the bonding with the support substrate appears to be unnecessary and a waste. Noted that LEDs to meet the required bins standard is often the challenge to most of the manufacturers when competing among one another. Therefore, promoting the yield rate of LEDs and cost-down is always the important issue to each LED maker.